If you have the newer iPhone 3GS model you’ll have to use an untethered jailbreak, since this is the only solution that is available. This new unlock process will update the baseband that currently exists to the new version. After you’ve updated your iPhone to this new baseband, you won’t be able to downgrade to the older baseband. In addition, when you update to the new baseband, you will void the warranty on your iPhone because Apple will soon learn about it. In the future, if any crucial updates become available, you should update to the new baseband. Therefore, there is no reason why you shouldn’t update your iPhone now, unless and until, you don’t want to update it in the future. With the newer firmware versions that start from 4.2.1, you won’t be able to restore your iPhone back to the original firmware, and you will have to use a custom IPSW file.
Download the newest 4.2.1 firmware for your iPhone and also download application Red Snow from redsnOw 0.9.6b6. When you download the firmware file, be sure that you don’t open it with iTunes or extract the file in any manner, simply save it. Extract the application Red Snow to a file folder.
If you don’t have the newest 4.2.1 firmware installed on your iPhone, launch iTunes and connect your iPhone and after your iPhone has been detected by iTunes, disregard any messages that may tell you to update the firmware. Press the Shift key after selecting your iPhone and then click on restore iPhone. This will permit you to choose the file that contains the firmware manually. Look in the folder where the respective firmware was downloaded to. Click on that file and press the choose button. This may take a few minutes. After your iPhone has been restored to the newest firmware, you can begin the process to jailbreak your iPhone with the Red Snow software.
To launch the red snow application, double click the file labeled redsnOw.exe. After the application has started, you will see a window that will have a message that will ask you to choose the file containing the desired firmware. Press Browse and choose the firmware file for your iPhone that you downloaded earlier.
Now you will be asked, if your iPhone is an older version or the newer version. If your iPhone 3GS is an older version no, else click yes. Red Snow will now verify your iPhone firmware. After the firmware is successfully verified, click on next. The data required to jailbreak your iPhone will be prepared by Red Snow. In some time there will be different options for you to select from. Ensure that you choose the Install Cydia option. If you want to install your custom logo, then click on the box titled Custom Recovery Logo and Custom Boot Logo. Finally, to continue, click on the next button. In a window you will be asked to confirm, if you want to upgrade your iPhone baseband to iPad baseband 06.15. If you select yes you can continue with the jailbreak process. If you select no you won’t be able to unlock your iPhone. The baseband for the iPad will be chosen automatically when you select yes.
Turn your computer off and connect it to your iPhone and then click on the next button. You will now have to place our iPhone in DFU mode. Once you have done this, Red Snow will automatically begin to download the iPad baseband on to your iPhone. Your iPhone will reboot itself once this process is done. Simply wait until your iPhone gets done with the jailbreak process and Cydia will be on your iPhone Spring Board, which can then be used to unlock your iPhone.